In a millimeter wave communication system, adopting a high carrier frequency for data transmission may make average path loss higher than that of an LTE system. For example, if a carrier frequency of 28 GHz is adopted for transmission, the following formula is utilized:
            L      f        =                  (                              4            ⁢            π            ⁢                                                  ⁢            R                    λ                )            2        ,
where R is a coverage radius of a cell, is a wavelength of a corresponding carrier and Lf is a path loss value.
Average proportion information of a high-frequency path loss value and an LTE path loss value is calculated to be:
                    L        H            ⁢              /            ⁢              L        L              =                                        (                                          4                ⁢                π                ⁢                                                                  ⁢                R                                            λ                H                                      )                    2                /                              (                                          4                ⁢                π                ⁢                                                                  ⁢                R                                            λ                L                                      )                    2                    =                                    (                                          λ                L                                            λ                H                                      )                    2                ≈        100              ,
LH represents the high-frequency path loss value and LL represents the LTE path loss value.
In order to ensure coverage, namely meet a minimum Signal to Interference plus Noise Ratio (SINR) requirement on a receiving side in high-frequency communication, it is necessary to increase sender and receiver gains.
            P      r        =                            P          t                ⁢                  G          t                ⁢                                            G              r                        ⁡                          (                              λ                                  4                  ⁢                  π                  ⁢                                                                          ⁢                  R                                            )                                2                    =                        P          t                ⁢                  G          t                ⁢                  G          r                ⁢                  /                ⁢                  L          f                      ,
where Gt is a sending antenna gain, Gr is a receiving antenna gain, Pt is sending antenna power and Pr is receiving antenna power.
LTE communication requires area coverage which maximally reaches 100 km, and area coverage of high-frequency communication may maximally reach 1 km if only average path loss (an open area) is considered according to maximum coverage. If characteristics of air absorption (oxygen absorption, carbon dioxide and the like), rain attenuation, shadow fading sensitivity and the like of an actual high-frequency carrier are considered, coverage which may actually be supported is smaller than 1 km.
If high-frequency communication supports maximum coverage of 1 km, an SINR different from that of an LTE system may be obtained for the same coverage area, and a signal to noise ratio of the former is at least 20 dB lower than that of the latter. In order to ensure that high-frequency communication and the LTE system have approximate SINRs within the same coverage, it is necessary to ensure an antenna gain of high-frequency communication. High-frequency communication has a smaller wavelength, so that accommodation of more antenna elements on a unit area may be ensured, and more antenna elements may provide a higher antenna gain, thereby ensuring coverage performance of high-frequency communication.
Accommodation of more antenna elements means that a beamforming manner may be adopted to ensure coverage of high-frequency communication, and a narrower beam requires more accurate beam alignment of a sender and a receiver. From an LTE-related design concept, it can be seen that achieving a better beamforming effect requires channel state information to be accurately obtained, thereby obtaining a beamforming weight from the channel state information. For obtaining a better beamforming weight, a second communication node serving as a receiver is required to feed back downlink channel state information or weight for a first communication node serving as a sender, and for the receiver, the sender is required to feed back uplink channel state information or weight, so that it is ensured that the first communication node may send a downlink service by adopting an optimal beam and the second communication node may also send an uplink service by adopting an optimal beam. In such a case, there may exist the following problem: the first communication node may not cover the receiver by utilizing the optimal beam before obtaining the weight, so that the receiver may not measure a reference signal sent by the first communication node, or although the first communication node covers the second communication node, the first communication node may not learn about a content fed back by the second communication node which may not reach the same coverage of the first communication node, so that beam weight selection and normal communication may not be performed.